Process for producing polyarylene sulfide

ABSTRACT

There is disclosed a process for producing a polyarylene sulfide (PAS) which comprises reacting a sulfur source with a dihalogenated aromatic compound in the presence of an aprotic organic solvent, characterized in that the process comprises at least one polymerization reaction step wherein a polymer phase as a dispersed phase is in the form of spherical droplets. It is made possible by the continuous polymerization process to discharge the polymer phase and solvent phase from a polymerization vessel at a constant ratio and as a result, to maintain PAS composition (concentration) at a constant level at all times, and thus to provide a continuous PAS production process which is effective for enhancing its molecular weight and stabilizing the same.

TECHNICAL FIELD

[0001] The present invention relates to a process for producing apolyarylene sulfide. More particularly, it pertains to a process forproducing a polyarylene sulfide which is high-quality, inexpensive,minimized in variation in molecular weight, and thus stabilized in thecase of producing a polyarylene sulfide which is useful in the fields ofelectronic materials, electrical materials, automobiles and heatresistant materials.

BACKGROUND ART

[0002] A polyarylene sulfide (hereinafter sometimes referred to as“PAS”), especially polyphenylene sulfide is known as an engineeringplastic which is excellent in mechanical strength, heat resistance,flame retardancy, solvent resistance and the like and which has goodelectrical characteristics and high rigidity. Thus it is widely employedas a variety of materials such as automobiles parts, electronic parts,electrical parts and mechanical parts.

[0003] Such PAS resin as stated above has hitherto been produced by abatch process, but there has recently been an increasing demand forcontinuous polymerization process for the sake of improvement in theproduction efficiency. There are disclosed as a continuouspolymerization process, for instance, U.S. Pat. Nos. 4,056,515,4,060,520, 4,066,632 and the like. However, any of the above-disclosedprocess involves the problem in that the molecular weight of the PASthus obtained is markedly low.

[0004] On the other hand, there is proposed for the purpose ofincreasing its molecular weight, a continuous polymerization processwherein a phase separation agent (water, sodium acetate, an alkali metalsalt or the like) is used to separate into a polymer phase and a solventphase ( refer to Japanese Patent Application Laid-Open No. 169844/1997(Heisei 9).

[0005] In the case of continuous polymerization process wherein such aphase separation agent is used, there is such a problem thatpolymerization reaction liquid becomes a phase separation state in whicha polymer phase and a solvent phase are separated from each other, thepolymer phase settles owing to difference in specific gravity in a placedifficult to be influenced by shearing force due to stirring and thelike such as the bottom of a polymerization vessel and inside of piping,thereby for instance, making it impossible to keep the compositionalratio (concentration) of polymer phase/solvent phase at a constant levelduring the transfer of the polymerization reaction liquid, and as aresult variation in the polymer concentration in the polymerizationvessel leads to variation in the the molecular weight, thus making itdifficult to produce PAS which is stabilized in its molecular weight.

[0006] With regard to the above-mentioned problem, the process in theforegoing Japanese Patent Application Laid-Open No. 169844/1997 (Heisei9) in which a proposal is made of a method for separately withdrawingthe polymer phase and solvent phase fails to sufficiently cope with theabove-mentioned problem because of the use of a special shape of areactor, a complicated piping structure, difficulty in flow rate controland the like factors. In such circumstances, it has been eagerly desiredto develop a continuous polymerization process which uses a phaseseparation agent and which is capable of discharging the polymer phaseand solvent phase from a polymerization vessel at a constant ratio andas a result, maintaining the PAS composition (concentration) in thepolymerization vessel at a constant level at all times.

DISCLOSURE OF THE INVENTION

[0007] The present invention has been made in the light of the subjectas mentioned above. An object thereof is to establish a continuouspolymerization process for producing PAS which is capable of dischargingthe polymer phase and solvent phase from a polymerization vessel at aconstant ratio and as a result, always maintaining PAS composition(concentration) in the polymerization vessel at a constant level andwhich is effective for enhancing and stabilizing ite molecular weight.

[0008] In view of the above-mentioned subject, intensive extensiveresearch and investigation were accumulated by the present inventors. Asa result, it has been found that the object of the present invention canbe achieved by sphering polymer phase droplets in the substantialpolymerization step during the continuous production of PAS. Thus thepresent invention has been accomplished on the basis of the foregoingfindings and information.

[0009] Specifically, the present invention provides a process forcontinuously producing a polyarylene sulfide which comprises reacting asulfur source with a dihalogenated aromatic compound in the presence ofan aprotic organic solvent, characterized in that said process comprisesat least one polymerization reaction step wherein a polymer phase as adispersed phase is in the form of spherical droplets.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

[0010] In the following, more detailed description will be given of thepresent invention.

[0011] In the present invention, the process for continuously producinga polyarylene sulfide comprises reacting a sulfur source with adihalogenated aromatic compound in the presence of an aprotic organicsolvent, and is characterized in that said process comprises at leastone polymerization reaction step wherein the reaction system isseparated into two phases including a polymer phase and a solvent phase,and the polymer phase is the dispersed phase in the form of sphericaldroplets. Specifically, the present invention relates to a continuouspolymerization process wherein whole polymerization operation is putinto practice either by single stage or by multistage wherein thepolymerization reaction liquid is transferred in turn throughpolymerization vessels connected in multistage, including the feed ofstarting materials for polymerization, a solvent and the like, andwithdrawing of a production system.

[0012] The present invention is characterized in that the processcomprises at least one polymerization reaction step wherein the polymerphase is the dispersed phase in the form of spherical droplets. A methodfor forming such spherical droplets is not specifically limited, but isexemplified, for instance, by a method wherein a phase separation agentand an aprotic organic solvent are fed in a reactor prior to the startof continuous polymerization, a method wherein spherical droplets areformed in a reactor in advance through batch polymerization underprescribed conditions, and the like method.

[0013] The continuous polymerization step is carried out usually at 230to 280° C., preferably 240 to 270° C . The temperature, when being lowerthan 230° C., sometimes results in failure to form spherical droplets,whereas the temperature, when being higher than 280° C., sometimesbrings about decomposition of the polymer.

[0014] By the term “spherical” as mentioned herein is meant to includenot only exact sphere but also ellipsoid, a form similar thereto and aform substantially close to sphere in which the sphere, ellipsoid or thelike is deformed in part.

[0015] Examples of the phase separation agent include lithium chloride,sodium acetate and a salt of an alkali metal such as lithium, water andthe like, of which lithium chloride is preferably used in particular.

[0016] Examples of the aprotic organic solvent include in general,aprotic organic polar solvents such as amide compounds, lactamcompounds, urea compounds, organosulfur compounds and cyclicorganophosphorus compounds, which can be used as single solvent or amixed solvent.

[0017] The above-mentioned amide compounds among aprotic organic polarsolvents are exemplified by N,N-dimethylformamide; N,N-diethylformamide;N,N-dimethylacetoamide; N,N-diethylacetoamide; N,N-dipropylacetoamide;N,N-dimethylbenzoic acid amide, etc.

[0018] The aforesaid lactam compounds are exemplified byN-alkyl-caprolactam such as caprolactam; N-methylcaprolactam;N-ethylcaprolactam; N-isopropylcaprolactam; N-isobutylcaprolactam;N-n-propylcaprolactam; N-n-butylcaprolactam; andN-cyclohexylcaprolactam; N-methyl-2-pyrrolidone(NMP);N-ethyl-2-pyrrolidone; N-isopropyl-2-pyrrolidone;N-isobutyl-2-pyrrolidone; N-n-propyl-2-pyrrolidone;N-n-butyl-2-pyrrolidone; N-cyclohexyl-2-pyrrolidone ;N-methyl-3-methyl-2-pyrrolidone; N-ethyl-3-methyl-2-pyrrolidone;N-methyl-3,4,5-trimethyl-2-pyrrolidone; N-methyl-2-piperidone;N-ethyl-2-piperilidone; N-isopropyl-2-piperidone;N-methyl-6-methyl-2-piperidone; N-methyl-3-ethyl-2-piperidone, etc.

[0019] The aforesaid urea compounds are exemplified by tetramethylurea;N,N′-dimethylethyleneurea; N,N′-dimethylpropyleneurea, etc.

[0020] The aforesaid organosulfur compounds are exemplified bydimethylsulfoxide; diethylsulfoxide; diphenylsulfone;1-methyl-1-oxosulfolane; 1-ethyl-1-oxosulfolane; 1-phenyl-1-oxosulfolaneetc.

[0021] The aforesaid cyclic organophosphorus compounds are exemplifiedby 1-methyl-1-oxophosfolane; 1-n-propyl-1-oxophosfolane;1-phenyl-1-oxophosfolane, etc.

[0022] Any of the above-exemplified aprotic organic polar solvent can beused alone or by mixing with at least one other or by mixing with asolvent which is not cited above and does not impair the object of thepresent invention so as to enable the mixture to be used as theforegoing aprotic organic solvent.

[0023] Of the various aprotic organic solvents as exemplified above arepreferable N-alkylcaprolactam and N-alkylpyrrolidone, among whichN-methyl-2-pyrrolidone (NMP) is particularly preferable.

[0024] The content of the above-mentioned phase separation agent in theaprotic organic solvent in the present invention is not specificallylimited provided that it meets the condition that the polymer phase isseparated, and it is usually 0.05 to 3.0 mole, preferably 0.2 to 2.5mole based on one mole of sulfur atom in the sulfur source. The contentof the phase separation agent, when being less than the above lowerlimit, sometimes brings about difficulty in forming spherical polymerphase.

[0025] There is no specific limitation on the continuous polymerizationprocess according to the present invention including the order of addingthe starting material components, except the conditions as describedhereinbefore. In the case however, where the aprotic organic polarsolvent containing a phase separation agent is incorporated with asulfur source such as lithium sulfide and polymerizing material such asdihalogenated aromatic compound or PAS with low molecular weight, it isnecessary that reaction liquid becomes a phase separation state in whicha polymer phase and a solvent phase are separated from each other, thatis to say, both the polymer phase and the solvent phase be in the formof liquid phase, and separated from each other.

[0026] In the present invention use is made of as a sulfur source, analkali metal sulfide, an alkali metal hydrosulfide, hydrogen sulfide andthe like, of which lithium sulfide is particularly preferably used. Anyof the sulfur sources can be used when necessary, in combination with analkali metal hydroxide.

[0027] The above-mentioned dihalogenated aromatic compound is notspecifically limited. It is preferably exemplified by a well knowncompound which is employed for producing a polyarylene sulfide, and isspecifically exemplified by dihalogenated benzene such asm-dihalogenated benzene and p-dihalogenated benzene, alkyl-substituteddihalogenated benzene, cycloalkyl-substituted dihalogenated benzene andthe like such as 2,3-dihalogenated toluene; 2,5-dihalogenated toluene;2,6-dihalogenated toluene; 3,4-dihalogenated toluene; 2,5-dihalogenatedxylene; 1-ethyl-2,5-dihalogenated benzene;1,2,4,5-tetramethyl-3,6-dihalogenated benzene;1-n-hexyl-2,5-dihalogenated benzene; and 1-cyclohexyl-2,5-dihalogenatedbenzene, aryl-substituted dihalogenated benzene such as1-phenyl-2,5-dihalogenated benzene; 1-benzyl-2,5-dihalogenated benzene;and 1-p-toluyl-2,5-dihalogenated benzene, dihalobiphenyl such as4,4′-dihalobiphenyl, dihalonaphthalene such as 1,4-dihalonaphthalene;1,6-dihalonaphthalene; and 2,6-dihalonaphthalene, and the like.

[0028] Two halogen atoms in these dihalogenated aromatic compound areeach fluorine, chlorine, bromine or iodine, and may be the same as ordifferent from one another. Of these, are preferable dihalogenatedbenzenes, and are particularly preferable those containing at least 50mole % of p-dichlorobenzene. The blending amount of the dihalogenatedaromatic compound based on hydrogen sulfide is set on 0.5 to 2.0,preferably 0.9 to 1.3 expressed in terms of the molar ratio ofdihalogenated aromatic compound/sulfur atom. The molar ratio, when beingless than 0.5, sometimes causes decomposition of PAS, whereas the molarratio, when being more than 2.0, results in a high recovery cost of thedihalogenated aromatic compound.

[0029] The number of moles of the dihalogenated aromatic compoundcontained in one liter of the aprotic organic solvent is set on 0.8 to4.0 moles, preferably 1.2 to 3.7 moles. The number of moles, when beingless than 0.8, sometimes gives rise to a sharp decrease in the molecularweight of PAS along with difficulty in controlling the same, whereas thenumber, when being more than 4.0, sometimes brings about a decrease inthe molecular weight of PAS, thus making it impossible for the resin toachieve physical properties of a practical level. The blending ratio ofeach of the components is expressed by the ratio of flow rate ( weight,number of moles or the like) of each of the components that are allowedto flow into a prescribed vessel ( the same holds in the followingdescription).

[0030] It is possible in the present invention to add, to the reactionsystem when necessary, a branching agent such as a halogenated aromaticcompound containing active hydrogen, a polyhalogenated aromatic compoundhaving at least three halogen atoms in its one molecule and apolyhalogenated aromatic nitrile compound that are properly selected foruse, in addition to the foregoing dihalogenated aromatic compound.

[0031] As mentioned hereinbefore, the continuous polymerization step iscarried out usually at 230 to 280° C., preferably 240 to 270° C. Theother reaction conditions are not specifically limited, but may be inaccordance with the conditions as disclosed in publicly knownliteratures such as Japanese Patent Application Laid-Open No.248077/1994 (Heisei 6 ).

[0032] For instance, the retention time of a polymerizing material orPAS with a low molecular weight that are allowed to flow in a continuouspolymerization vessel, although varies depending upon the flow rate ofeach of the components as well as the shape and size of the vessel, isset on 0.1 to 20 hours, preferably 0.1 to 10 hours, particularlypreferably 0.1 to 5 hours.

[0033] In the present invention, the number of stages that are usable inthe polymerization vessel, which is not specifically limited, may bemultistage wherein the temperature condition may be altered per stage.It is preferable in the case of multistage that in at least onepolymerization vessel including the final stage vessel, the polymerphase be in the form of spherical droplets. Particularly preferably, thepolymer phase in every vessel is in the form of spherical droplets. Inthe present invention, the phase separation agent needs only to be addedto at least one polymerization vessel including the final stage vessel,and it is preferably added to every vessel with a view to maintain thechemical composition in all the polymerization vessels at a constantlevel.

[0034] The polymerization vessel and an agitational impeller that areused in the present invention are not specifically limited, but thepolymerization vessel is preferably of the type well suited for completemixing, and the agitational impeller is preferably a large size impellersuch as a full zone impeller.

[0035] As the starting material to be of service in the presentinvention, the foregoing sulfur source such as lithium sulfide and thedihalogenated aromatic compound may be used as such, but is preferablysubjected to preliminary polymerization in a continuous or batchwiseprocess with a view to obtain PAS with a high molecular weight.

[0036] The preliminary polymerization, which is not specificallylimited, is put into practice by adding a dihalogenated aromaticcompound, water and an aprotic organic solvent to the reaction productcontaining lithium sulfide, and preserving the mixture at 180 to 220° C.for 0.1 to 10 hours, preferably 1 to 6 hours in a continuous step.Preferably, the blending amount of each of the components satisfies thefollowing requirements.

[0037] The number of moles of the dihalogenated aromatic compoundcontained in one liter of the aprotic organic solvent is preferably 0.8to 4.0 (moles/liter), more preferably 1.2 to 3.7 (moles/liter). Theblending amount of the dihalogenated aromatic compound based on 1 moleof lithium sulfide is preferably 0.5 to 2.0 moles, more preferably 0.9to 1.3 moles. The ratio by weight of water to the aprotic organicsolvent (water/aprotic organic solvent) is preferably at least 3/97,more preferably in the range of 5/95 to 15/85.

[0038] Subsequently, the substantial polymerization procedure asmentioned hereinbefore is carried out by using the the starting materialfor polymerization or the resultant PAS with a low molecular weight.

[0039] The polymerization solution obtained after the substantialpolymerization can be subjected to cleaning operation by adding waterthereto to the extent that the PAS is not solidified. The amount ofwater, which varies depending upon the amount and the temperature of thepolymerization solution, may be such an amount that the PAS is notsolidified nor precipitated by overcooling. It is preferable to usuallyagitate the content in a cleaning tank so that the polymerizationsolution and water are sufficiently mixed with each other.

[0040] A cleaning solution is not specifically limited provided thatimpurities or by-products which are stuck to the polymer do not exertadverse influence on the polymer by being dissolved in the cleaningsolution. Examples of the cleaning solution include methanol, acetone,benzene, toluene, water and NMP, of which water is preferable.

[0041] The polymerization solution after the completion of thepolymerization reaction is sent to a separation tank, where the solutionis subjected to a separation procedure to separate it into a polymerphase and a solvent phase.

[0042] A process for converting the solvent phase thus separated(consisting essentially of NMP, water and LiCl) into lithium sulfide vialithium hydroxide is disclosed, e.g. in Japanese Patent ApplicationLaid-Open No. 319009/2000 (Heisei 12), etc.

[0043] For the purpose of assuring more sufficient effect on cleaningand separation, the steps of cleaning and separation are preferablyrepeated optional plural times.

[0044] In the present invention, since the polymer phase in which thesteps of cleaning and separation have been completed still contains asolvent, it is preferable to remove the solvent. The solvent removalmethod is not specifically limited, but may be in accordance with a wellknown solvent removal method which is used in the production of PAS, forinstance, a flashing method disclosed in Japanese Patent ApplicationLaid-Open No. 33878/1995 (Heisei 7).

[0045] The PAS in which the solvent removal procedure has been completedcan be taken out in a molten state or in the form of granule after beingsolidified by cooling using a proper cooling method. The cooling methodis exemplified by air cooling, water cooling, oil cooling and the like.

[0046] It is enabled by the simplified process according to the presentinvention to readily and steadily produce a polyarylene sulfide whichhas a sufficiently high molecular weight, an intrinsic viscosity [η] ofat least 0.10, preferably at least 0.13, a melt index [MI] of 0 to 1000g/10 minutes, and as the case may be, has gel forming property. Inaddition, variation in the intrinsic viscosity with the lapse of time oramong the batches upon the production of the polymer is markedlyimproved, wherein the intrinsic viscosity is measured with a Ubbellohdeviscometer for 0.4 deciliter/g solution of the polyarylene sulfideobtained by the foregoing process in α-chloronaphthalene at 206° C.

[0047] In the case where the polyarylene sulfide (PAS) obtained by theprocess according to the present invention is molded into any of avariety of products, the PAS can be properly and optionally incorporatedat need with an other polymer, pigments, graphite, metallic powders,glass powders, quartz powders, talc, calcium carbonate, glass fibers,carbon fibers, fillers such as various whiskers, stabilizing agents,release agent, etc.

[0048] By the process according to the present invention which comprisesat least one polymerization reaction step wherein a polymer phase as adispersed phase is in the form of spherical droplets, it is madepossible to establish a method capable of discharging the polymer phaseand solvent phase from a polymerization vessel at a constant ratio andas a result, maintaining PAS composition (concentration) at a constantlevel at all times, and thus to provide a continuous PAS productionprocess which is effective for enhancing its molecular weight andstabilizing the same.

[0049] In what follows, the present invention will be described in moredetail with reference to working examples, which however shall neverlimit the present invention thereto.

EXAMPLE 1

[0050] Preparatory Polymerization

[0051] A one m³ titanium-made starting material synthesis vesselequipped with a stirrer was charged with 554 kg ofN-methyl-2-pyrrolidone(NMP) and 100 kg (2.38 kilomole) of lithiumhydroxide (LiOH.H₂O), and the resultant mixture was heated to and keptat 140° C. The water contained in the lithium hydroxide as a startingmaterial was removed by batch distillation. Thereafter, 65 n-kiloliterof gaseous hydrogen sulfide was blown into the mixture at a temperaturekept at 130° C. to synthesize lithium hydroxide.

[0052] Subsequently, blowing of hydrogen sulfide was stopped, and thesynthesis vessel was again heated to raise the temperature up to 205° C.Accompanying the temperature rising, the water by-produced on blowinghydrogen sulfide was removed by batch distillation, while lithiumsulfide was produced from lithium hydrosulfide.

[0053] After the completion of the reaction, the reaction productcontained 1.08 kilomole of lithium sulfide and 0.214 kilomole of lithiummetylbutylate. To the reaction product was added 165.1 kg (1.123kilomole) of p-dichlorobenzene (PDCB) and further 583 kg (0.32 kilomole)of pure water to proceed with reaction at 210° C. for 3 hours. Then thereaction liquid was cooled to 60° C. or lower, and the resultantreaction mixture was taken out from the reactor into a 20 liter vessel.The conversion of the PDCB was 85%.

[0054] Substantial Polymerization

[0055] A 10 liter autoclave equipped with a full zone impeller wascharged with 855 g of lithium chloride as a phase separation agent and5145 g of NMP, and was heated to raise the temperature up to 260° C. Theabove-prepared prepolymer was preserved at 60° C. and was continuouslysupplied to the reactor at a flow rate of 33.3 g/minute by the use of agear pump.

[0056] On the other hand, about 150 to 200 g of the polymerizationliquid was withdrawn from the reactor through a withdrawing nozzle every5 minutes approx. so as to maintain the liquid at a constant level. Theprocedure was continued for 24 hours, while the dispersion state wasvisually confirmed by the use of a microscope, and molecular weight ofthe polymer was determined by measuring the intrinsic viscosity [η]. Theresults are given in Table 1. The intrinsic viscosity thereof wasmeasured with a Ubbellohde viscometer for 0.4 deciliter/g solution ofthe polyarylene sulfide (PAS) in α-chloronaphthalene at 206° C., the PAShad been cleaned with a large quantity of water and dried.

EXAMPLE 2

[0057] A 10 liter autoclave equipped with a full zone impeller wascharged with 10 mole (459.4 g ) of lithium sulfide, 10 mol ( 1470.1 g)of p-dichlorobenzene, one mole (41.96 g ) of lithium hydroxidemonohydrate, 4 mole (72.1 g) of water and 4.3 liter of NMP. Theresultant mixture was heated to 260° C. for 30 minutes under stirring at125 r.p.m. and subsequently was allowed to react for 2 hours.

[0058] Thereafter, the prepolymer which had been obtained in the samemanner as in Example 1 was added to the above-obtained reaction liquid.Thus continuous substantial polymerization was carried out and theobjective product was evaluated in the same manner as in Example 1. Theresults are given in Table 1.

COMPARATIVE EXAMPLE 1

[0059] The procedure in Example 1 was repeated to synthesize PAS andevaluate the same except that lithium chloride feeding was omitted. Theresults are given in Table 1. TABLE 1 Time (hour) 3 6 9 12 15 18 21 24Ex. 1 [η] 0.27 0.28 0.28 0.28 0.28 0.28 0.28 0.28 Disper A A A A A A A AEx. 2 [η] 0.28 0.28 0.28 0.28 0.28 0.28 0.28 0.28 Disper A A A A A A A AC/ [η] 0.25 0.28 0.22 0.25 0.28 0.20 0.22 0.25 Ex. 1 Disper B B B B B BB B

INDUSTRIAL APPLICABILITY

[0060] The polyarylene sulfide obtained by the production processaccording to the present invention can be preferably utilized as amaterial for a variety of molded articles, for instance, a material forfilms, fibers, mechanical parts, electrical parts, electronic parts andthe like.

1. A process for continuously producing a polyarylene sulfide whichcomprises reacting a sulfur source with a dihalogenated aromaticcompound in the presence of an aprotic organic solvent, characterized inthat said process comprises at least one polymerization reaction stepwherein a polymer phase as a dispersed phase is in the form of sphericaldroplets.
 2. The production process according to claim 1, wherein thepolymerization reaction step is carried out at a temperature in therange of 230 to 280° C.
 3. The production process according to claim 1,wherein a phase separation agent and an aprotic organic solvent are fedin a reactor in advance, and thereafter the continuous polymerizationreaction step is carried out.
 4. The production process according toclaim 1, wherein the phase separation agent is lithium chloride.
 5. Theproduction process according to claim 1, wherein the aprotic organicsolvent is a N-alkylcaprolactam or a N-alkyl-pyrrolidone.
 6. Theproduction process according to claim 1, wherein a sulfur source and adihalogenated aromatic compound are batch polymerized in advance in anaprotic organic solvent, so that a polymer phase is brought to sphericaldroplets, and thereafter the continuous polymerization reaction step iscarried out.
 7. The production process according to claim 1, wherein apreliminary polymerization is carried out.
 8. The production processaccording to claim 7, wherein the preliminary polymerization is carriedout at a temperature in the range of 180 to 280° C.